1. Field of the Invention
The present invention relates to a method of self-diagnosing a mobile telephone set for use in a mobile telephone switching system, and particularly to a method of self-diagnosing a read-only memory (hereinafter referred to as ROM) which is provided within the mobile telephone set.
2. Description of the Related Art
In mobile telephone sets, various self-diagnoses are carried out when the power supply is turned ON. The reliability of mobile telephone sets is improved by preventing their use unless the mobile telephone sets are determined to be normal as a result of the self-diagnoses. The self-diagnoses include a diagnosis for a ROM provided within the telephone sets, which must be carried out without fail. In this case, the contents of all the addresses of the ROM are read out to carry out operations such as summing up or logic calculus exclusive OR. If each operational result turns out to be a value previously calculated, then the content of the ROM are determined to be normal, while, if not, then it is determined that something abnormal exists within the contents of the ROM and the user is informed of that fact.
Incidentally, in recent mobile telephone sets, as the program size of the man-machine interface portion has been increased in order to achieve various functions, the capacity of the ROM has been correspondingly increased from 512 kbits to 1 Mbit. As a result, there has arisen a problem in that it takes a long time for diagnosis if, each time the power supply is turned ON, the contents of all the addresses of the ROM are read out for operation, and the result of this operation is compared with a specific value so as to diagnose the ROM. For example, a typical eight-bit microprocessor (hereinafter referred to as a CPU) takes about 1 to 2 seconds for the diagnosis. Accordingly, takes about 1 to 2 seconds until the telephone set becomes operable after the power supply is turned ON, which could cause irritation to the user and, therefore, results in a serious problem so as to impair the reputation of the mobile telephone switching system. In addition, as a result of the time period required for diagnosis, since the telephone set cannot be tested for about 1 to 2 seconds after the power supply is turned ON, the number of man-hours required for inspection is increased thereby resulting in an increase in manufacturing cost for the manufacturer.